Monolithic metal structure



A ril 14, 1953 A. B. BAGSAR MONOLITHIC METAL STRUCTURE File d Nov. 20,1948 FIG. 2

FIG.

INVENTOR. A A RON 8. BA GSAR ATTORNEYS Patented Apr. 14, 1953 2,634,699MONOLITHIC METAL STRUCTURE Aaron B. Bagsar,

Oil Company, of New Jersey Application November 20, 1948,

4 Claims.

The development of fusion welding has resulted in its successfulapplication to various monolithic steel constructions. An earlyapplication was to structures such as pressure vessels, after which theshipbuilding industry adopted this method of construction as asubstitute for the riveted type of construction. The welding method hasalso been applied to a certain extent to bridges and other massivestructures.

The known advantages of the welded over the riveted constructioninclude: considerable weightand material-saving effected by eliminatinglapped seams; appreciably stronger seams obtained by welding, since theriveted construction requires drilling or punching through thestructural members; no maintenance problems involved similar to rivetedseams, such as leaks occurring through rivet holes due to corrosion orexcessive flexing, etc., obtaining a flush job, thereby simplifyinginternal drainage and painting problems and obtaining a stream-linecontruction, thereby reducing frictional loss.

However, in certain all-welded constructions of monolithic type, certaindifliculties have developed that were not foreseen and which in somecases have had serious consequences, such difficulties beingcharacteristic of those monolithic steel structures which are subject tomultiaxial and severe stresses. For example, in ship constructionserious fractures were encountered, because a normally ductile steelwould exhibit a brittle fracture in a welded ship, due to complexity ofthe stresses imposed by construction and by the service conditions,these fractures mostly occurring in the plates and not in the welditself. In order to minimize these difficulties it was later proposed toinsert in certain critical sections riveted seams in order to break upthe continuity of the plates in the welded structures and also to obtaina certain amount of flexing, the purpose being to at least arrest theextent of cracking. It has also been proposed to add numerous structuralmembers to the ships structure, mainly internally, in order to relievethe welded shell of the ship from excessive stresses, with the object ofthereby preventing cracking of the hull and decking. Both the aboveremedies have distinct limitations and disadvantages. They may reduce,but do not eliminate, the danger of losing a ship by fracturing of thehull.

Insertion of riveted seams in critical sections of the ship isdistinctly objectionable, since riveting requires drilling of the mainshell at these sections in order to install rivets, thereby serious-Drexel Hill, Pa., assignor to Sun Philadelphia, Pa., a corporationSerial N0. 61,255

1y reducing the strength of the section. This modification is alsoobjectionable for the reason that most of the stresses are thrown ontothese riveted seams, because the remainder of the shell and decking iscontinuous by virtue of the fact that the plates are welded together anddo not therefore flex as much as the riveted joint. Still anotherobjection to this expedient is that the rivets in these insertions leakbadly after a short service; which may be due to the excessive flexingand stressing that are induced in these seams, since the remainder ofthe shell is welded and continuous. These stresses are therefore moresevere than in a wholly riveted shell, since in the latter such stressesare more evenly distributed over a munber of riveted joints.

The insertion of independent members in the ship to stifien the shipsstructure is also objectionable because of the difiiculty of installingthe sections in such a manner and with such rigidity as to make theseadditional sections share proportionately the stress simultaneously withthe remaining members of the ships structure. In the circumstances, thehull fails first before the stress is transmitted to these additionalstifieners, or in other cases the stifieners fail first and transmit thestress to the ships shell, thereby rendering the stiffeners inefiective.

It is known that riveted seams are not as susceptible to crackpropagation as welded ships of monolithic type, and that cracks may bearrested in these riveted seams, although failure of riveted seamsthemselves by cracking is not altogether uncommon. It is believed thatthe virtue of the riveted seam in this respect over the Weldedconstruction is attributable to the fact that no excessive stressconcentrations are possible because of the relative flexibility of theriveted seam, and also to the inherent geometry of the riveted seam inwhich the adjoining plates are not made integral with each other, as inwelding, but are held together mechanically by rivets and butt straps orby the lapping arrangement.

In welded bridge and other massive constructions,a1so,similar defectsexist and similar serious fracturing has resulted, which, in the opinionof some engineers, make the application to bridges and other massivestructures of fusion welding impracticable, notwithstanding therecognized advantages of such type of construction. Even pressurevessels of the welded monolithic type, such as gas storage tanks, arenot immune to the dangers above outlined, which are not satisfactorilyremediable by any of the above specified expedients that break up thecontinuity of the plates. In fact the application of butt-welding, asdistinguished from riveting, to structural steel generally,notwithstanding its pronounced advantages over riveting, has beenrestricted and, in some proposed applications, prevented, by the specialdefects above set forth.

Regardless of all the care exercised to eliminate welding imperfectionsand to improve workman ship, some irregularities will be present in thecompleted welded construction, such as imperfect weld penetration,misalignment, inclusions in the Welded seams, weld undercutting, andcertain discontinuities in the steel plates themselves which aredifficult to eliminate altogether, such as scratches, arc craters,segregations or laminations. The loci of such imperfections act as focalpoints from which cracks may start, and unless some means is provided toarrest them, these cracks will assume serious proportions. In the caseof a ship a single crack may wholly incapacitate it or even cause it tobreak into sections.

The object of my invention is to arrest the extension of shearing ortearing fractures of local origin while avoiding the limitations anddisadvantages of both the riveted and welded construction and of theexpedients heretofore adopted having the same object. I have found thata metal plate composed of certain materials other than plain carbonsteel (which is utilized in welded ship construction and in otherstructures of the welded monolithic type) and which, unlike plain carbonsteel, will not become brittle and will maintain a high degree ofductility at low temperature, will effectively resist cracking orfracturing under stresses that will readily propagate a crack throughcarbon steel. A ship hull or deck composed entirely of plates of suchmaterial would efiectively resist cracking or fracturing; but many ofsuch compositions would be subject to deteriorating conditions to whichsteel is resistant and all of such compositions are so relativelyexpensive that, if they were equal to steel in all other respects, thecost would be prohibitive. I have discovered, however, that even when asingle plate of such composition is applied to a monolithic welded steelplate structure, it will arrest, beyond its locus of application, theadvance of any crack that is propagated through a contiguous multi-platesteel structure. Compositions suitable for such applied units are knownto the metallurgist and are too numerous to detail; but as examples maybe cited copper, brass, nickel-copper, and many alloy steels such aschromium steel, nickel steel and nickelchromium steel. All thesematerials are characterized by a pronounced degree of ductility attemperatures as low as any that might be reasonably expected to beencountered by a ship, pressure vessel, storage tank, bridge, etc., or(say) any temperature down to or even below minus 50 F. At the abovetemperature, what is known as plain or ordinary carbon steel ofcommerce, composed almost or entirely of iron, carbon, manganese andsilicon, disregarding an almost negligible quantity of impurities suchas phosphorus and sulfur, has no measurable ductility, whetherdetermined by elongation or bending tests, at a low temperatureapproaching minus 50 F.

Plates of this character may be inserted between the conventional steelplates and buttwelded thereto, or they may be applied to the interior orexterior face of the monolithic steel structure, and they may or may notbe protected from contact with water or other fiu'id to which they maybe subjected by enclosing or overlapping plates of steel.

The invention may best be understood by reference to the followingdescription of the attached drawings, in which Fig. 1 is a plan view ofthe deck of a ship.

Fig. 2 is a transverse vertical sectional view taken along the line 2-2of Fig. 1 or along any transverse line across the area of the deck orhull desired to be protected.

Fig. 3 is a cross-sectional view of a special plate or strip interposedbetween and welded to adjacent conventional steel plates.

Fig. 4 is a cross-sectional view of another embodiment of the inventionin which a special plate or strip is applied to one or more conventionalsteel plates.

In Figs. 1, 2 and 3, the plates marked a are conventional plates ofcarbon steel, while the plates or strips marked 1) are special unitsinterposed between, and butt-welded to, the conventional plates. Eachspecial unit is of a composition, other than carbon steel (which at lowtemperature becomes brittle and is non-resistant to cleavage fracture),that maintains its ductility at any temperature to which the ship hullmight be exposed. There are a great number of metals that maintain theirductility, that is, are nonbrittle, and hence are not subject tocleavage fracture, at a temperature below that specified, say, safelybelow minus 50 F., for example, copper, brass, or a nickel-copper alloy,or, in fact, many alloy steels, such as chromium steel, nickel steel,nickel-chromium steel and molybdenum bearing steels. Metallurgists wellknow that carbon steel loses its ductility when exposed to temperaturesno lower than that which a ship normally encounters in service and theyalso know that there are various metal elements and metal alloys thatretain their ductility no matter what low temperature it may be expectedto encounter in service. If the entire hull of the ship were composed ofplates having the ductility of said special units, as, for example,stainless steel, the danger of transverse cracking or fracturing wouldbe obviated; but many of such substitute metals or alloys would not besuitable for various reasons, and any that would be suitable would becommercially impracticable, since the cost of such a construction wouldbe prohibitive. I have found, however, that if the described specialstrips extend, as indicated in Fig. 1, longitudinally of the ship acrossthe area desired to be protected, but occupying a very minor width ofthe hull and deck, the resistance to cracking or fracturing in thedirection indicated by the arrow is efiectual; that is, the crack willextend through a conventional plate or plates until it meets a specialunit, when it encounters a bar rier through and beyond which it cannotproceed. Such a crack or fracture usually starts at or near the anglebetween the hull and the deck, but wherever it starts it cannot extendentirely across the hull or deck.

While two long special strips b applied to the deck (if the deck is tobe protected) and two long strips b applied to the hull afford adequateprotion, it is desirable to apply additional long strips 0, especiallyto the hull. It isnot necessary, however, that each of the special unitsshall be a lon strip extending entirely along the protected area. Forsuch long special strips may be substituted, or to such long specialstrips may be added, a number of relatively short units, marked d. so

distributed (preferably staggered as indicated) as to extend along aplurality of parallel lines extending longitudinally of the ships hullacross the area to be protected and thus adapted to intersect any lineextending transversely of the ships hull within that area. While inFigs. 1 and 2 these short units are shown as applied only to the deck,the protection of the hull from cracking or fracturing is of primaryimportance. These short strips are not in these figures shown as appliedto the hull in order to avoid the confused showing that would resultfrom overlapping of full and broken lines.

It is practicable, also, to confine the strips of special metal betweenstrips of steel, so that only steel is exposed at the interior andexterior surfaces of the null or deck, but this specific modification isnot claimed, but forms the subject matter of an application filed ofeven date herewith, Serial No. 61,256.

Instead of interposing such special units b, or c, or d, between theconventional plates and buttwelding them thereto, as shown in Fig. 3,special plates or strips 6 of the special composition above describedmay be applied to the face (either exterior or interior) of the hull and(or) deck and welded thereto as shown in Fig. 4. Such special plates orstrips may be distributed as illustrated in Fig. l at b, c and d and asdescribed in specifying the distribution of inserted special buttweldedstrips or plates. These special plates may overlap adjacent conventionalplates, but this is not necessary, nor in fact desirable, especially inthe construction of new ships, since separate conventional plates, withthe special units applied thereto, may be fabricated before they arewelded. in place.

These special units may be provided with holes or slots, as disclosed inmy application filed July 31, 1947, Serial No. 765,007, but such amodification is unnecessary, since, if the special units are of acomposition that maintains pronounced ductility at low temperatures, itis unnecessary for the special units to present edges, not fused to theshell, extending longitudinally of the body of the ship.

What I claim and desire to protect by Letters Patent is:

1. A construction for the shell of a ship comprising a multitude ofplates of plain carbon steel and welded joints by means of which saidplates are secured together to form a monolithic structure, in whichshell cracks that may develop tend to extend in one general direction,namely, transverse to the longitudinal axis of the shell, saidconstruction also comprising a number of special metal strips, of acomposition other than plain carbon, that maintain ductility at atemperature substantially below that at which plain carbon steel losesits ductility, welds uniting said strips to certain of said plates ofplain carbon steel, said strips extending longitudinally of the axis ofthe shell, and thus transverse to said general direction, along aplurality of spaced apart lines one or more of which intersect any linetransverse to the longitudinal axis of the shell within the area of theshell designed to be protected, to thereby arrest, and prevent theextension of,

any crack that may spread in such general direction.

2. A construction as defined in claim 1 in which the special metalstrips are of substantially the same thickness as the plates of plaincarbon steel to which they are welded and are applied by insertion inthe shell with their opposite faces substantially aligned with theopposite faces of plates of plain carbon steel adjacent thereto "andwhich are butt-welded to said plates.

3. A construction as defined in claim 1 in which the plain carbon steelplates within the designed protected area are imperforate and in whichthe special strips welded to the shell are applied to one face of theshell.

4. A construction for the shell of a ship comprising a multitude ofplates of plain carbon steel and welded joints by means of which saidplates are secured together to form a monolithic structure, in whichshell cracks that may develop tend to extend in one general direction,namely, transverse to the longitudinal axis of the shell, saidconstruction also comprising a number of special metal strips, of acomposition other than plain carbon steel, that maintain ductility at atemperature substantially below that at which plain carbon steel losesits ductility, welds uniting said strips to certain of said plates ofplain carbon steel, said special strips extending longitudinally of theaxis of the shell and thus transverse to said general direction, eachlongitudinal arrangement constituting a unit and each strip being of alength that is short relative to the length of that area of the shellthat is designed to be protected from crack extension, adjacent sides ofsaid strips spaced apart, said units being arranged along a number oflines, extending longitudinally of the axis of the shell, that aretransversely spaced apart, said special units being of such length thatthey are transversely opposite spaces between special units extendingalong other lines and are also transversely opposite ends of suchspecial units extending along other lines and are thus in staggeredrelation, whereby any line transverse to the longitudinal axis of theshell within such area designed to be protected intersects one or morespecial units and is thus adapted to arrest, and prevent extension of,any crack that may spread in such general direction.

AARON B. BAGSAR.

References Cited in the file of this patent UNITED STATES PATENTS

